Rit (Vísindafélag Íslendinga) - 01.07.1962, Side 90

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larger mass including the rhyolite hill Laugarfell close to
Great Geysir. The main rock above the rhyolite is horizon-
tally stratified brown tuff which is considerably altered and
might he considered as part of an “old” element. It has a
thickness of over 200 m and can he traced to a height of 600 m.
It is at places a very hard mudstone, fractured and infilled.
After the present slope, cut into these rocks, had been
formed, young volcanic activity started on the top of the
mountain. A layer of breccia with scarse bombs and lava
lumps, but mainly consisting of bomh fragments was formed.
Fig. 45. Bjarnarfell, eastem slope.
R = rhyolite; B = volcanic breccia layer; L = basalt lavas.
The layer has probably flowed, so that intense crumbling
and disintegration of bombs would take place. This layer
covers most of the slope, from the edge at 600 m down to
350 m, where it has covered a former gully which was near-
ly identical with the present Hellisgil. This shows the youth-
fulness of the breccia and suggests upper Pleistocene age.
The volcanic activity continued with lava flows that covered
the flat surface of the mountain and flowed over the rim
down into the slope. The lower parts of these lava flows have
been wiped out by glaciers but some flows can be traced suf-
ficiently far down to show the true picture.
At some places fresh horizontal lavas and a fresh volcanic
breccia cover the rhyolite directly and reach a height of more